DESCRIPTION (adapted from the application) Disorders of cardiac function have provided the most direct evidence of iron toxicity, and cardiac failure has been the most common cause of death in patients with hemochromatosis. We have shown that even mild iron-overload promotes injury to the postischemic heart. We also showed that the beta-blocker propranolol could accumulate in endothelial lysosomes and provide both cellular and cardiac protection against oxidative injury. This application is based upon two hypotheses: 1) Lysosomes in the endothelial cells are major storage sites of iron and provides a primary source of releasable redox active low molecular iron, which can enhance cardiovascular injury in response to oxidative stress (e.g. ischemia/reperfusion and exogenous oxidants). 2) Stabilization of lysosomal iron by selected lipophilic beta-blockers prior to oxidant stress will attenuate cellular and cardiac injury. By using both the cultured endothelial cell and rat heart models, we propose to investigate the following aims: 1) Determine the contribution of lysosomal iron to endothelial cell and cardiac injury due to iron-overload and subsequent oxidative stress. 2) Determine if alkalinization of lysosomes by selected beta-blockers and analogs will be accompanied by decreased oxidative stress in the iron-loaded endothelial cells. 3) Determine if treatment with beta-blocker analogs will attenuate oxidative stress in hearts from iron-loaded rats. 4) Assess if long-term pre-treatment with the drugs reduce cellular and tissue iron accumulation. A variety of sophisticated techniques will be employed to assess free radical production and oxidative injury (ESR spin trapping, lipid peroxidation products and antioxidant quantification), total and low molecular iron quantification (X-ray microanalysis, Calcein fluorescent-indicator, NO-ESR technique), and tissue and cellular toxicity (myocardial function and cell survival). We believe our proposed studies may lead to a reassessment of the potential use of beta-blockers for iron-overload therapy.